The expression "shaped charges" is understood to mean charges for directed bursting or hollow charge effect. These charges consist of an explosive charge enclosed in a container or case and defined, forwardly in the direction of the intended effect by inlays or liners which are of a concave bulging, conical or trumpet-shape. On detonation of the rearwardly located explosive charge, these liners or inlays are converted into particle jets or more or less projectile-like slugs which, at supersonic speeds, are flung forwards in the intended effect direction of the charge. It is primarily the shape and material of the liner or inlay that which determines whether the main effect of a shaped charge is of the nature of a jet or a projectile. The most common material used for the liner or inlay is pure copper, but other metals such as iron, spent uranium, aluminium and tantalum have also been employed.
Ammunition must be capable of withstanding extreme temperature variations without its function being tangibly affected. As long as the shaped charge inlays were made of pure copper and the rest of the case surrounding the explosive charge was of steel, problems of temperature variation were not excessively difficult to solve, since steel and copper do not, after all, have all too different coefficients of thermal expansion.
However, now that there is a steady trend towards producing shaped charge inlays from tantalum in order to satisfy the demands placed on the efficiency of the charge, the problem of temperature variation becomes more acute. In particular, as the shaped charge inlays are intended to be permanently mounted in the steel case which generally surrounds the explosive charge portion included in the shaped charge on all sides except in the intended effect direction where the inlay or liner forms the concave cavity in the explosive substance that gives rise to the directed explosive effect. The reason for this is that tantalum and steel display large differences in thermal expansion. Previously, the inlays have normally been secured in shaped charges by means of a screw ring threaded in the mouth of the steel case and fixedly clamping the inlay against a folded edge in the case. Provided that the clearance between the wall of the case and the inlay is not too large, this securement method gives the permanent securement of the inlay that has been deemed necessary for the satisfactory functioning of the shaped charge. However, it is known in the art that the reforming of the inlay into a projectile or particle jet on detonation of the explosive charge is affected by the anchorage ring and the securement fold along that edge zone which, as it were, is shielded from the explosive since this does not reach all the way out to the outer edge of the inlay.
Now that the inlay is to be manufactured of tantalum, as this material gives an amplified effect as compared with the previously used copper, and the rest of the sleeve surrounding the explosive is made of steel, a clearance of 0.01 mm between inlay and case at .about.20.degree. C. would cause the inlay to suffer from a subsequently permanent change in shape if the charge were to be exposed to a temperature of -40.degree. C., a circumstance which must be considered as fully conceivable at any rate in cold climates such as in Sweden.
If greater clearance is to be permitted between the inlay and case, the folded edge and the screw ring fixedly clamping the inlay must be given a larger surface area which, in both cases, means parameters that negatively influence the effect of the charge on the target, as a larger portion of the inlay will then be shielded from the explosive.